Certain turbojets are provided with post-combustion devices by which an additional thrust may be given in certain special circumstances, especially during jet-assisted take-off. The air passing through the turbojet is separated upstream of the post-combustion device into one internal stream of hot air and one external stream of cold air concentric to the hot air stream. Pivoting flaps may be used in double-flow engines so as to adjust the dilution rate, both in cases of functioning where post-combustion is inactive and in those cases where post-combustion is ignited, generally by modifying the conditions or junction locations of the two streams.
One example of the prior art exists in the French patent application No. 2 626 044 in which the pivoting flaps have a double function of masking or uncovering a fuel injection ramp while creating in the latter state an excess pressure making it possible to supercharge scoops with cold air, these scoops directing this air towards fuel injection radial arms traversing the internal stream.